1. Field of the Invention
The present invention relates to a process for the preparation of olefinically unsaturated isocyanates from certain, preferably cycloaliphatic, polyisocyanates and certain olefinically unsaturated, preferably monohydric, alcohols; the isocyanates obtained in accordance with this process; and their use as a binder component in one-component coating compositions.
2. Description of the Invention
One-component coating compositions based on prepolymers containing NCO-functional urethane groups are known (Houben Weyl, Methoden der Organischen Chemie [Organic chemistry methods], Vol. E 20, page 1646, Georg Thieme Verlag 1987). They are prepared by reacting organic polyisocyanates with high molecular weight, high functionality polyols, in particular polyether polyols and/or polyester polyols. The high molecular weight provides these compositions with good film-forming properties and results in good optical properties for the film. The high molecular weight also results in higher viscosity, which means that the prepolymers can only be utilized as paints or in coating compositions if they are greatly diluted or contain a considerable proportion of monomeric diisocyanate.
High monomeric diisocyanate concentrations are, however, physiologically unacceptable. The utilization of large quantities of solvent is also not acceptable for environmental reasons. The gap between a high molecular weight, high functionality prepolymer having a high viscosity but providing excellent properties, on the one hand, and low molecular weight, low viscosity products having unsatisfactory solution stability and drying properties, on the other hand, cannot be closed with the NCO-functional prepolymers.
In addition to NCO-functional coating resins, one-component systems which can be cross-linked by oxidation are also known (Ullmann, Enzyklopadie der technischen Chemie [Encyclopaedia of industrial chemistry], 4th edition, Vol. 19, pages 75 et seq., Verlag Chemie Weinheim, Deerfield Beach Fla., Basle 1980). These polymeric compounds may additionally also contain urethane groups (DE-OS 4,011,376). If these urethane resins which cross-link by oxidation have higher molecular weights, relatively fast-drying, tough paint systems result. However, considerable quantities of solvent or reactive thinner are required for these resins.
Admittedly, reactive thinners such as those described in EP-A 0,301,345 exhibit, without solvent, relatively low viscosities, but they must be used in combination with considerable quantities of high molecular weight compounds, such as alkyd resins, to obtain workable coating compositions. Their film-forming properties when they are used as the only resin component are totally unsatisfactory, and the low molecular weight structure results in unsatisfactory and excessively slow drying.
Ester group-containing reactive thinners, such as those described in EP-A 0,301,345, are unsuitable for applications in the construction sector, because there is a danger that the ester group, which is highly vulnerable to hydrolysis, will rapidly dissociate on basic substrates such as concrete.
An object of the present invention is to provide low-viscosity resins for solvent free or low solvent-containing coating compositions which have good technical properties and rapid chemical drying at room temperature and which may be applied in a universal and physiologically acceptable manner.
This object may be achieved using the process according to the invention which is described below in greater detail. The resulting products satisfy the requirements for the simultaneous presence of olefinic double bonds, urethane groups and isocyanate groups. For this a balanced ratio of urethane groups, isocyanate groups and double bonds which may be cross-linked by oxidation is particularly essential.